(a) Field of the Invention
The present invention relates to a liquid crystal display and, more particularly, to a liquid crystal display which achieves stable operation by thermally isolating the liquid crystal from the external environment.
(b) Description of the Related Art
Generally, liquid crystal displays experience a common characteristic wherein the alignment directions of the liquid crystal molecules can be changed in accordance with a change in an applied electric field. This characteristic gives the liquid crystals the ability to control light in a specific way and makes them suitable for use in display devices.
With advances in micro-electronics technology which have made portable systems feasible, tho liquid crystal display has been highlighted as a thin and light low-powered display device.
FIG. 2 is a cross-sectional view showing the structure of a conventional liquid crystal display. The liquid crystal display 15 includes upper and lower substrates 1 and 3 spaced apart a predetermined distance, conductive layers 5a and 5b coated on inner surfaces of the upper and lower substrates 1 and 3, respectively, and facing each other, a liquid crystal 7 injected between the conductive layers 5a and 5b, sealants 9 for bonding the upper and lower substrates 1 and 3, together, and upper and lower polarizer films 11 and 13 each attached on outer surfaces of the upper and lower substrate 1 and 3, respectively.
The upper and lower substrates 1 and 3 are formed with transparent glass materials and spaced apart from each other to thereby form a gap between them. The liquid crystal 7 is injected into the gap through an injection inlet (not shown).
The conductive layers 5a and 5b are formed with indium tin oxide (ITO) materials and constitute horizontal and vertical electrode patterns. The cross-point of the horizontal and vertical electrode patterns becomes a pixel. In operation, the conductive layers 5a and 5b are applied with voltage from an external driving circuit (not shown).
Meanwhile, the upper and lower polarizer films 11 and 13 are adjusted perpendicular to each other in their polarization axes.
As the liquid crystal 7 is injected into the gap between the upper and lower substrates 1 and 3, it is twisted by 90.degree. with respect to the substrates 1 and 3. Thus, when a voltage is applied to the conductive layers 5a and 5b, molecules of the liquid crystal 7 reorient themselves perpendicular to the substrates 1 and 3 to thereby control the transmittance of light passing through them. That is, the linearly polarized light that has passed through the upper polarizer film 11 is unable to pass through the lower polarizer film 13.
However, in the conventional liquid crystal display 15, the liquid crystal 7 is easily affected by external temperature changes and does not keep its liquid crystalline phase at relatively higher or lower temperatures. That is, the liquid crystal 7 retains much of its crystalline properties at relatively higher temperatures. Thus, the molecule alignment of the liquid crystal 7 is changed slowly under an applied voltage and, as a result, the response time becomes slower.
On the contrary, at relatively lower temperatures, the liquid crystal 7 retains much of its liquid properties. Therefore, the birefringence of the liquid crystal 7 bearing a refractive index in the long axis direction and a refractive index in the short axis direction cannot be uniformly kept. As a result, the desired molecule alignment of the liquid crystal 7 is not maintained resulting in a picture image with degraded contrast.